(1) Field of the Invention
The present invention relates to a device for predicting and analyzing an inundation phenomenon that causes flood disaster. More specifically, the present invention relates to an inundation simulating system that simulates a process of water flowing from a river into an urban area using a computer and displays spatial information obtained from the simulation on a computer display.
(2) Description of the Related Art
Recently, in order to mitigate natural disasters, an attempt to predict such disasters has been drawing attention. To predict natural disasters, a simulation with a computer has proven effective. In the simulation, the prediction variables in the calculation grid/grids represent the disaster state, and changing of the prediction variables by time based on the physical rule represents the disasters changed in time. As an example of the simulation, an inundation simulation in which water overflowing from the river and flooding the city is known. In the inundation simulation, the calculation grids are arranged in the city. The variables representing the flood velocity and the water depth placed on the calculation grids are changed based on the physical rule called “shallow water equations”. In the inundation simulation, boundary conditions must be set. The boundary conditions are a bank breach section or inflow sections, or an overflowing section. Hereinafter, the conditions about the inflow sections are called “bank breach conditions”, assuming the bank breach is a typical cause of overflow from the river.
For example, a “real time dynamic inundation simulation system” described in Patent Document 1, JP-A-2004-197554, discloses the invention relating to a system for realizing the inundation simulation. That enables a user to specify one point on a map displayed on the display of the system as a bank breach point and set the bank breach conditions on the calculation grids arranged over the point. The bank breach conditions of the system include a length of the bank breach along the river bank, a water level at the bank breach and a height of the bank breach. The bank breach point is the representative point of the bank beach, the length of the bank breach is the length of the bank breach along the river, the water level of the bank breach is the water level at the bank breach point and the height above sea level of the bank breach is the height above sea level at the bank breach point.
In the conventional simulation system, the bank breach conditions are given to one point on a map as shown in the Patent Document 1.
In the conventional simulation system, however, problems described below occur.    1. The bank breach length, which is one of the bank breach conditions, is only represented by a numeral value, and a user cannot visually recognize the length of the bank breach. Thus, the user may set an unrealistic value for the bank breach length.    2. The direction of the flow quantity at the bank breach flow (the flow quantity that passes the inflow section), which is one of the bank breach conditions, is not decided automatically.    3. The bank breach length must be shorter than the calculation grid intervals. In other words, the bank breach conditions in which the bank breach covers over a plurality of calculation grid/grids cannot be input.
The problems are caused by the bank breach being approximated with a representative point and a length. If the length of the bank breach is short enough relative to the size of the calculation grid/grids, then the approximation does not cause a significant error. Generally, it is known that the length of the bank breach at a middle size river in Japan is about 50 to 200 m. In the conventional inundation simulation, the size of the calculation grid/grids is set at about 250 m because if the size of the calculation grid/grids is too short, the calculation does not complete in a practical time period.
In order to perform highly accurate simulation, the calculation grid/grids need to be short. If the length of the bank breach is equal to or longer than the size of the calculation grid/grids, an error due to approximation cannot be ignored.